When the running string for a tubular production string to be cemented has a conduit or cable running through it making it impossible to push wiper darts through the running string a mechanism to exhaust contaminated trailing interface fluids to the annulus and launch the liner wiper plug needs to be below the running string. One such design was described in detail in US Publication 2010/0181079 and the relevant teachings therein are incorporated by reference herein as if fully set forth. Basically the liner wiper plug 38 shown in FIG. 1 was supported from a support housing with shear pins 64 extending into a housing or boss 63 above the liner wiper plug 38. The housing or boss 63 for the shear pins 64 was secured internally in the production string 36. Initially the stinger or extension 62 was in a bore through the plug 38 so cement could be pumped past the plug to the lower end of the production string 36 and out the bottom and up a surrounding open hole annulus. Fluid was spotted behind the cement to push the cement down toward the plug 38. Since the fluid and the cement were not isolated from each other, some of the cement at the tail end became contaminated and it was desirable to stop pumping before any contaminated cement reached the lower end of the running string 34. At that point the running string was picked up to pull out the extension 62 from the plug 38 which would allow one or more flappers such as 66 to slam shut and further fluid pumping would then circulate out the contaminated cement which was then possible because the seal 68 was no longer in the deployment sleeve 56. After the circulation of the contaminated cement, the running string 34 and tool 32 were run back in to reengage seal 68 and the pressure is built up on the closed flapper valve 66 to break the shear pins 64 and launch the plug 38 into the production string 36 until the plug 38 bumps at the lower end as shown in FIG. 2. The fluid 50 is pumped behind the plug 38 to bump it. Meantime the good cement ahead of the plug is advanced further up the annulus 48 while displacing wellbore fluids ahead of the cement toward the surface at 42. All cement above the production string is circulated out of the well. After cement hardens around the production string it can then be perforated and produced.
There were several issues with the above described process. One was the cost of the wiper plug assembly 38 that generally included a plurality of flappers 66. This was a very expensive device to build. More significantly the boss 63 that supported the shear pin that in turn held the liner wiper plug assembly in position remained behind inside the production string 36 and presented a reentry restriction and a flow choke point to later production. Alternatively going in and milling it out in a separate trip was time consuming and expensive.
The present invention solves that problem by providing a support for the liner wiper plug on the running tool rather than in the string being run. The wiper plug has a open passage through it that can be closed with a releasable dart this is also supported in the running tool at a point above the liner wiper plug. The dart is temporarily supported so that flow can bypass around it and go through the open bore in the liner wiper plug. When the cement is pumped and the contaminated cement is to be circulated out, the running tool is picked up to deploy extendable dogs. A set down with the dogs on the top of the production string shifts a sleeve to remove support for the dart allowing it to move downward to plug off the bore in the liner wiper plug. A subsequent pickup force pulls upper seals 130 out of the production string and exposes a lateral port above the landed dart and circulation can get the contaminated cement back to the surface through the annulus. Setting back down again reengages the seals 130 and closes the lateral port and allows a pressure buildup to release the liner wiper plug with the dart in it so that the cement is displaced from the string being cemented and into the surrounding annulus. The liner wiper plug is retained to the running tool with shear pins or collets in the running tool. When the running tool is pulled, there are no longer any restrictive bosses internally in the cemented string to restrict access or throttle subsequent production. Those skilled in the art will more readily appreciate more aspects of the invention from a review of the detailed description of the preferred embodiment and the associated FIGS. 3-7 while understanding that the full scope of the invention is to be found in the appended claims.